Sensitivity of bronchoprovocation and tracheal mucous velocity in detecting airway responses to O₃

This study was undertaken to determine whether measurements of tracheal mucous velocity or airway reactivity to inhaled carbachol more sensitively detect airway effects of inhaled ozone (O ₃) in conscious sheep. Dose-response curves of mean pulmonary flow resistance (RL) to carbachol were obtained by measuring RL after five breaths of carbachol aerosol with stepwise increases in drug concentration. The animals then breathed 0.5 ppm O ₃ through an endotracheal tube for 2 h. The dose-response curves were repeated immediately after the 0.5 ppm O ₃ exposure and 24 h later. In the eight sheep studied, there were no significant alterations in base-line RL immediately after or 24 h after 0.5 ppm O ₃. Airway hyperreactivity was not apparent immediately after the sheep breathed 0.5 ppm O ₃, but it was evident 24 h later. In contrast, six sheep that breathed 0.5 ppm O ₃ in the same manner for 2 h did not show a significant depression in tracheal mucous velocity the same day or 24 h later. Exposure to 1 ppm O ₃ for 2 h resulted in airway hyperreactivity immediately after the exposure and elevated base-line RL 24 h later, 2 ppm O ₃ produced an increase in base-line RL immediately after exposure. We conclude that, in conscious sheep, airway hyperreactivity appears to be a more sensitive indicator of airway effects produced by short-term exposure to 0.5 ppm O ₃ than depression of tracheal mucous velocity.